1. Field of the Invention
The present invention relates generally to electroluminescence, and more particularly, to a novel method of producing a thin fluorescent film for electroluminescence for use, for example, within the manufacture of an electroluminescent cell.
2. Description of the Prior Art
Conventional methods of producing thin fluorescent films for electroluminescence generally employ the embedding process or other heat-treating processes, wherein activators, such as for example, Al, Ag, Au, Cu, Mn and Pb, and coactivators, such as for example, NaCl, ZnCl.sub.2, NH.sub.4 Cl, NH.sub.4 I, Al, Cu and Ga, are added to base materials, such as for example, ZnS, ZnSe and CdS, so as to form evaporated films. However, such conventional methods have several disadvantages in that they cannot produce fluorescent films for electroluminescence which emit light by the action of direct current, unless coactivators are in fact added thereto as mentioned above. For example, a fluorescent film produced by the addition of only Mn, as an activator, to a base material of ZnS, can emit light as a result of the application of AC voltage thereto, however the same does not emit light as a result of the application of DC voltage thereto. It is well known, however, that a fluorescent film, produced by means of the addition of Cu, Ce, or the like, as a coactivator, as well as an activator of Mn, to a base material of ZnS, can emit light by means of an application of DC voltage.
It is also evident that if the evaporation process or the like, which is utilized to vapor-deposit a base material, such as for example, ZnS upon a base plate, such as for example, a glass plate, is simultaneously or alternately used with the ionization injection process which ionizes and accelerates an activator, such as for example, Mn and then injects the ions thereof, a fluorescent film for electroluminescence can in fact be obtained which emits light as a result of the application of DC voltage thereto without adding the above-mentioned coactivators, such as for example, Cu and Ce. However, such a method has several disadvantages in that it requires a complicated and expensive apparatus provided with an ionization-injection mechanism in addition to a vacuum evaporation mechanism which is extremely difficult to operate.